A new theory of aortic root function has been developed. It is suggested that the opening and closing of the aortic leaflets is accomplished by dimensional changes in the aortic root. This permits the leaflets to move from the closed to the open position, with minimal flexion and with no change in length. In order to test this hypothesis the aortic roots of animals will be marked at critical points and their motion recorded with image intensification. The motion of the aortic root and the leaflets will be correlated with changes in aortic pressure and flow.